On the Moon

On the Moon

Exhibition Text

These three moon rocks, unlike all the other samples in this hall, were collected from beyond Earth by human hands—during the Apollo lunar missions.

The Moon’s long memory

The craters on the Moon are a historical record of asteroid impacts—on Earth as well as the Moon.

For the last three billion years, asteroid impacts have been almost the only event to shape the Moon's surface. Unlike Earth, the Moon has no life, and almost no geologic activity or water. It also lacks an atmosphere, so it has no wind or weather.

Because the Moon's surface is so inactive, it has preserved a long history of asteroid impacts. The Moon and Earth are so close together that the two bodies share roughly the same history of asteroid bombardment. But whereas geology and erosion have erased most of Earth's craters, the Moon still shows traces of impacts that are billions of years old.

A violent birth

The Moon probably formed in the wake of a titanic collision between Earth and a smaller planet.

How did the moon form? The leading theory is that the Moon resulted from a glancing collision between the young Earth and an object the size of Mars.

Several observations about the Moon confounded early attempts to explain its origin. Most significantly, the Moon is much less dense than Earth, because it has a tiny iron core.

The Apollo missions showed that although the Moon has much less iron than Earth, it formed from the same original reservoir of materials. Yet on the Moon these ingredients are mixed in different proportions. In the late 1970s a few scientists came up with a theory that seems to explain the data-the Moon formed from debris spun off by the largest collision in Earth's history.